The present invention relates to the installation of sewer systems and the like. The invention is particularly directed to a sewer system structure known as a "sewer chimney" which joins a lower sewer main line to an upper sewer branch line. A sewer chimney is usually constructed as an appurtenance to a deep sewer to allow the branch line (building connections or lateral branch lines) to be installed at a shallower depth. These chimneys vary in height and in pipe size, but are typically used for a residence or small commercial building.
Concrete chimneys are typically built by pouring a concrete mix into a form on the job site. This technique produces defective sewer chimney structures as a result of incomplete drying, cracking and overload conditions on the mainline sewer unfavorable weather conditions; many of the problems which are associated with pouring concrete into a form can be avoided by prefabricating the sewer chimneys before they reach the construction site. The prefabricated sewer chimney includes several parts which are assembled at the construction site.
A common problem with such prefabricated concrete sewer chimneys is that parts may not seal properly due to voids in concrete or may vary in the sealing surface being irregular so as to prevent proper construction of the chimney. If the parts do not fit together perfectly, it is difficult or impossible to maintain water-tight seals between the parts.
In the prefab sewer chimney systems which are in current use, a short pipe or nipple extends upwardly from the main line fixture to a fixture in the bridge portion of the supporting base. There is a seal between the main line fixture and the bottom of the nipple, and a seal between the nipple and the bridge portion of the base. The seal in the bridge portion is a gasket which surrounds the upper end of the nipple and which permits relative movement between the nipple and the supporting base while maintaining a water-tight seal between the bridge portion of the base and the nipple. This is an important feature for ease of installation and for allowing for settling of the chimney structure after installation. The cap block at the top of the sewer structure has a built-in T-fixture. The T-fixture and the cap block includes a vertical bore which is vertically aligned with the nipple and the horizontal bore for receiving a service pipe. A captured seal unit is provided between each concrete structure of the chimney so that the system is water-tight from the "T" in the cap block to the main line fixture.
There are two problems which are associated with the nipple which extends from the main line fixture. If the nipple is too long relative to the seal in the bridge portion of the supporting base, there is always a standing volume of sewerage above the seal. Also, if the nipple is cut too long, the top of the nipple may impinge upon the riser section just above the bridge portion of the base, thereby putting pressure on the main line "T" or even structural failure of the mainline tee. This results in a leak at some point in the structure. Even if the riser does not impinge upon the riser section just above the bridge portion during installation of the chimney unit, subsequent settling of the chimney unit may cause the nipple to impinge upon the riser which is located just above the bridge portion creating problems as previously mentioned. If the nipple is too short, the nipple may not extend above the seal in the bridge portion which results in a leak.
There are many other factors which contribute to the failure of present day prefabricated sewer chimneys to maintain a water-tight seal. Although the prefabricated sewer chimneys include seals between each precast concrete section, the seals are often broken or damaged through carelessness of the workers during assembly, failure due to workers using the wrong size seal, or by the units being struck by boulders during the backfilling operation. Damage to these seals can also occur if the sewer chimney is struck by equipment during the installation of service laterals to the building which is being serviced. The placing of too much backfill on one side of the unit causes uneven stresses in the sewer chimney which can also result in damage to the seals. In many cases, the damage to the seals occurs during subsequent service work long after the intial installation of the unit.
Another problem which is associated with existing sewer chimney systems concerns the need to accommodate different types of service pipes. The service pipe specifications vary considerably from one locale to another and for each type of service installation. For example, two commonly used service pipes differ in wall thickness and in outside diameter so that a different block "T" must be used for each type of service pipe used. These and other difficulties experienced with the prior art devices have been obviated in novel manner by the present invention.
It is, therefore, a principal object of the invention to provide a precast sewer chimney which is substantially more resistant to loss of water-tight integrity than existing sewer chimney structures.
Another object of this invention is the provision of a precast sewer chimney which has the ability to accept service pipes of different diameters.
A further object of the present invention is the provision of a precast sewer chimney which can be effectively tested for water-tight integrity in or out of the unit during and immediately after installation of the structure.
It is another object of the present invention to provide a precast sewer chimney which can be effectively tested for water-tight integrity wherein if a leak does occur, it will be pinpointed for repair of the seal at that point.
A still further object of the invention is a provision of a precast sewer chimney structure which can be tested and put into immediate use during construction of the structure thereby eliminating by-pass pumping.
It is a further of the invention to provide a precast sewer chimney structure which has inner and outer sealing systems thereby greatly increasing the chances that the sewer chimney will maintain its water-tight integrity.
It is a further object of the invention to provide a precast sewer chimney structure which allows for settling of the chimney structure without losing its sealing effectiveness.
It is a further object of the invention to provide a method of installing a precast sewer chimney structure which can be installed easily, quickly and safely.
It is a still further object of the invention to provide a method of installing a precast sewer chimney structure which insures water-tight integrity of the structure.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.